9 times of out 10 the person in question does not realize that their problem has already been solved

True, but even if someone realises their problem has already been solved, they may not choose the best solution. One of the main problems facing Perl is that the first Perl code/tutorials/books people often encounter are badly written. Many newcomers learn Perl badly, but are unaware they're doing so.

If you choose to reinvent the wheel for any reason, point people towards better solutions. This prevents anyone using your code because they're unaware anything better exists.